Fulminating material application technique

ABSTRACT

A method of providing the primer anvil wire of a percussive-type photoflash lamp with a coating of a fulminating material in which the anvil wire is dipped into a body of fulminating material to a predetermined depth to provide a coating thereof on the anvil wire extending along its length a predetermined distance from one end thereof, the coating is dried and then the coating is electrochemically stripped from a segment of the wire extending from the coated end thereof to thereby provide an anvil wire having a coating of fulminating material disposed on a segment of predetermined length located intermediate the ends thereof.

United States Patent [72] Inventors Stephen V. Brown;

William C. Fink, both of Williamsport, Pa. [21] Appl. No. 886,999 [22] Filed Dec. 22, 1969 [45] Patented Oct. 26, 1971 [73] Assignee Sylvania Electric Products Inc.

[54] FULMINATING MATERIAL APPLICATION TECHNIQUE 7 Claims, 1 Drawing Fig.

[52] U5. Cl 204/146, 431/93 [51] Int. Cl 801k 1/00 [5 0-] Field of Search 204/146, 130,141;431/93-97 [56] References Cited UNITED STATES PATENTS 2,428,141 9/1947 Burkhardt 204/146 Primary Examiner-John H. Mack Assistant ExaminerT. Tufariello AnorneysNorman J. OMalley and Joseph C. Ryan ABSTRACT: A method of providing the primer anvil wire ofa percussive-type photoflash lamp with a coating of a fulminating material in which the anvil wire is dipped into a body of fulminating material to a predetermined depth to provide a coating thereof on the anvil wire extending along its length a predetermined distance from one end thereof, the coating is dried and then the coating is electrochemically stripped from a segment of the wire extending from the coated end thereof to thereby provide an anvil wire having a coating of fulminating material disposed on a segment of predetermined length located intermediate the ends thereof.

PATENTEDum 26 Ian w J Y WK a m NME E V A HMN mw m L FULMINATING MATERIAL APPLICATION TECHNIQUE This invention relates to the manufacture of photoflash lamps and more particularly to those of the percussive type.

Generally speaking a percussive-type photoflash lamp comprises an hermetically sealed, light-transmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussive-type photofiash lamp may comprise a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible such as shredded zirconium foil and a combustion-supporting gas such as oxygen. The primer comprises a metal tube and a charge of fulminating material on a wire anvil supported therein. Operation of the lamp is initiated by an impact onto the tube of the primer to cause deflagration of the fulminating material on the wire anvil up through the tube to ignite the combustible disposed in the lamp envelope.

The fulminating material generally comprises a mixture of red phosphorus, potassium chlorate and a powdered metal such as zirconium. It must be extremely sensitive to impact ignition to insure high lamp reliability of flashing with the desirably low-impact energies delivered by the firing mechanism. At the same time, the metal tube of the primer is thin-walled and soft so as to minimize the required impact and afford maximum lamp reliability.

Relatively early in the development of a percussive-type photoflash lamp of the general type shown in the accompanying drawings, the primer comprised a metal tube closed at one end and a wire anvil having a coating of fulminating material located thereon at one end thereof. Initially, the coated wire anvil was just dropped into the tube and it bottomed on the closed end thereof. This arrangement was never entirely satisfactory for several reasons, including accidental ignition during insertion and poor firing reliability due to variations in the positioning and ultimate location of the body of fulminating material. Subsequently several improvements were made both in the construction of the primer and the composition of the fulminating material.

Ultimately, the wire anvil was provided with a head on the end thereof which bottoms in the primer tube and lobes intermediate the ends thereof, with the body offulminating material located therebetween. Then when the anvil is placed in the tube with the head of the anvil bottoming in the closed end of the tube, the tube is crimped just above the head of the anvil thus positively anchoring it therein and the lobes stabilize the anvil within the tube.

A paint brush technique was initially employed in the application of fulminating material to the surface of the wire anvil. This method entailed painting a band of fulminating material onto a rotating anvil wire between the lobes and the head. However, this method proved to be too slow and was not adaptable to an automated process. It was also found that the weight and thickness of fulminating material on the anvil varied within limits not acceptable to the production of a percussive flashlamp. It was necessary to adopt a method of applying fulminating material in which a more nearly constant weight and thickness could be maintained and at the same time the process must be acceptable to automated production. The technique that meets these standards was a dip method in which the end of the anvil wire with the formed head is dipped into a liquid suspension of fulminating material a distance sufficient to coat the surface up to a point just below the lobes. The coating of fulminating material is then allowed to dry. This method of application necessitates the removal of fulminating material from the head and the lower portion of the anvil wire after it has been coated. This will prevent inadvertent ignitions of the fulminating material when a coated anvil wire is inserted into its primer tube and also provide a bare metal surface on the anvil wire to accept a crimp securing it to the tube.

Since the fulminating material contains a water base, it was initially felt that the head of the anvil wire, if coated with a hydrophobic substance, would prevent adherence of any fulminating material. The head of the anvil wire was coated with a hydrophobic substance such as silicones, or paraffin. However, this method proved unsuccessful. Approximately one out of every three anvil wires that was coated with a hydrophobic substance did not repel the fulminating material. This is probably due to the high viscosity and high solids content of the fulminating material suspension.

A second approach to the problem involved the use of ultrasonic cleaning as a technique. Anvil wires containing fulminating material were subjected to ultrasonic water baths, and it was found that in time all the material was stripped from the surface of the anvil. The anvil wire was dipped a specified depth into the ultrasonic bath. That portion of the fulminating material submerged into the bath was then cleaned from the anvil surface. However, this method proved to be quite slow; some anvil wires were not washed thoroughly even after 10 seconds of ultrasonic agitation. This is unacceptable to high speed production. Secondly, due to extreme agitation of the bath by the ultrasonic element, it is difficult to remove a constant length of fulminating material from each anvil wire.

Another method tried was that of removing fulminating material with a fine jet of water. The jet of water is directed onto the surface of the anvil wire to be cleaned. The force of the water striking the anvil surface removes the softened fulminating material. However, it was difficult to remove a consistent length of primer from each anvil wire. The force of the jet also caused droplets of water to splash onto the band of fulminating material not washed from the anvil surface. This caused extraction of the soluble components in the fulminating material, desensitizing it.

ln view of the foregoing, the principal object of this invention is to provide a practical and effective method of cleaning the tips of anvil wires coated with fulminating material prior to insertion into the primer tube of a percussive-type photoflash lamp.

We have found that a constant length of fulminating material can be effectively removed from the anvil wire by a method of electrolysis. This is accomplished within a time limit suitable to automated production without decreasing the sensitivity of the remaining material on the anvil surface. This technique is based on the electrolysis of water, where hydrogen is released at the cathode and oxygen is released at the anode. The anvil wire is made the cathode and that portion of the surface to be cleaned of fulminating material is submerged into the electrolytic solution. The water-based electrolyte penetrates the dry fulminating material and it appears that hydrogen bubbles are liberated between the surface of the anvil wire and the coating of fulminating material. This produces a high level of mechanical agitation which loosens the fulminating material from the surface of the anvil. The action takes place with such intensity that material is removed from the anvil surface in less than a seconds time. This process can be carried out anodically. However, only half the volume of gas is released at the anode as compared to the cathode. Therefore, a certain amount of mechanical action is lost with anodic washing and longer cleaning times are needed for removing fulminating material.

The electrolytic bath is composed of a salt, alkaline cleaner and wetting agent. Although many ionic salts could be used as conduction promoting electrolytes, there is an advantage in using potassium chlorate since it is a component of the fulminating material and its use in the electrolytic bath would inhibit leaching of the potassium chlorate from the fulminating material not to be removed during the electrolytic operation. Alkaline cleaners such as ammonium bicarbonate and trisodium phosphate may be added to the solution which enhance the wetting and penetration of the fulminating material. The alkaline salts also improve electrolytic conductivity. It is also desirable to add organic surface active agents or detergents to the solution which improves the surface activity and penetration of the alkaline cleaner. However, a high concentration of wetting agent may cause foaming which would prevent a constant liquid level from being maintained. Excessive lengths of fulminating material would be removed from the anvil wire making control more difiicult. The overall importance of what the electrolytic solution is composed of and the concentrations of its components is based on the fact that no sensitivity must be lost from the remaining fulminating material on the wire anvil after it is cleaned, and that the solution insures effective removal in a short period of time applicable to automation. One such solution which proved successful in these respects was composed of the following: potassium chlorate 1.0 gram per 100 grams of water), trisodium phosphate (0.10 grams per 100 grams of water), and sodium alkyl benzene sulfonate (0.01 grams per 100 grams of water).

Another salt solution which proved to be quite effective and which also has the advantage of sufficient electrical conductivity but avoids the initial use of potassium chlorate which is a rather hazardous material of relatively low solubility comprises the following composition: about lO percent sodium chloride, a little less than 90 percent water and traces of sodium 2-ethylhexylsulfate, a wetting agent, and an antifoaming material such as Balab No. 748 for example. However, the advantage of having the C ions in the solution is still maintained. The removed fulminating material which accumulates in the solution where the cleaning of the anvil is achieved contains potassium chlorate, which will dissolve in the cleaning solution and prevent a leaching out of the chlorate in the fulminating material remaining on the anvil wire.

There are other possible electrolytic solutions that could be used without departing from the nature of the invention. For example, sodium and ammonium bicarbonate have been used successfully. Oxidizing salts such as sodium perchlorate, and potassium nitrate could be employed. However, their use might affect the composition of the fulminating material remaining on the anvil wire, thereby decreasing its sensitivity. Since heating the solution promotes more rapid removal of material, it is preferred to maintain a solution temperature of about 50C.

Alternating or direct current may be used for the operation. However, direct current is desired, since alternating current reduces the evolution of hydrogen gas at the wire surface, and a corresponding amount of mechanical action is lost by its use. A rectified AC circuit can be used. Effective cleaning is obtained at voltage outputs of 1 volt or higher; 18 to 20 volts is preferred.

In the accompanying drawing, the single FIGURE is a sectional elevational view of a percussive-type photoflash lamp having a primer of the type with which the method of this invention may be employed.

The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constricted at one end to define an exhaust tip 4 and shaped to define a seal 6 about a primer 8 at the other end thereof. The primer 8 comprises a metal tube 10, a wire anvil 12 and a charge of fulminating material 14. A combustible such as filamentary zirconium l6 and a combustion-supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial within the primer tube [0 and insuring clearance between the fulminating material l4 and the inside wall of the tube 10. A refractory bead 24, fused to the wire anvil 12 just above the inner mouth of the primer tube It), eliminates bumthroughs and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer tube.

The method of this invention provides an anvil wire which can be safely inserted into the primer tube of a percussive-type photoflash lamp without inadvertent ignition of the fulminating material. The electrochemical stripping technique employed in the practice of this method insures that a closely controlled length of fulminating material will be removed from each anvil wire, while at the same time the remaining portion of fulminating material on the anvil surface is not deactivated. Thus it also provides a clean area around the anvil wire on which a crimp can be safely located to secure the anvil wire in its primer tube. In view of the speed with which the electrolytic process cleans the wire anvil, this technique is easily adapted to automatic, high-speed percussive flashlamp production.

What we claim is:

l. The method of providing a primer anvil wire of a percussive-type photoflash lamp with a coating of fulminating material thereon intermediate the ends thereof, said method comprising:

dipping said wire into a body of fulminating material to a predetermined depth to thereby provide a coating on said wire extending therealong a predetermined distance from one end thereof;

drying said coated wire;

and electrochemically stripping said coating from a segment of said coated wire extending a predetermined distance from the coated end thereof.

2. The combination of claim 1 in which the segment of the coated wire from which coating is to be stripped is dipped a predetermined distance into an electrolytic solution.

3. The combination of claim 2 in which the electrolytic solution comprises a salt, an alkaline cleaner and a wetting agent.

4. The combination of claim 3 in which potassium chlorate is a constituent of both the fulminating material and the electrolytic solution.

5. The combination of claim 2 in which the electrolytic solution comprises about 1 gram of potassium chlorate, 0.1 gram of trisodium phosphate and 0.0l gram of sodium alkyl benzene sulfonate, all per 100 gram of water.

6. The combination of claim 2 in which the solution is maintained at a temperature of about 50 C.

7. The combination of claim 2 in which said electrolytic solution comprises about 10 percent sodium chloride, a little less then percent water and traces of a wetting agent and an antifoaming material.

i t l i 

2. The combination of claim 1 in which the segment of the coated wire from which coating is to be stripped is dipped a predetermined distance into an electrolytic solution.
 3. The combination of claim 2 in which the electrolytic solution comprises a salt, an alkaline cleaner and a wetting agent.
 4. The combination of claim 3 in which potassium chlorate is a constituent of both the fulminating material and the electrolytic solution.
 5. The combination of claim 2 in which the electrolytic solution comprises about 1 gram of potassium chlorate, 0.1 gram of trisodium phosphate and 0.01 gram of sodium alkyl benzene sulfonate, all per 100 grams of water.
 6. The combination of claim 2 in which the solution is maintained at a temperature of about 50* C.
 7. The combination of claim 2 in which said electrolYtic solution comprises about 10 percent sodium chloride, a little less then 90 percent water and traces of a wetting agent and an antifoaming material. 